This project investigates endogenous and exogenous factors that contribute to the development of cognitive and social competencies during the first four years of life. Before children are old enough to enter formal social learning situations, nearly all of their experiences stem directly from interactions they have with their primary caregivers. Four conceptually distinct categories of caregiver-child interactions can be identified: nurturant, material, social, and didactic. These encompass much of the everyday behavior of infants' caregivers. In previous work using samples of convenience, the Principal Investigator linked the latter two types of caregiving to cognitive development in babies. In the present study set, this work is being replicated and extended by focusing on the extent to which three maternal characteristics (age, employment status, and parenthood status) and type of substitute care experienced during mother's employment influence the observed relations between caregiver social and didactit stimulation on the one hand and child cognitive and social competencies on the other. In addition, in a longitudinal extension of the study, the subjects are being revisited when they are 20 months old and 48 months old. At 20 months, measures of toddler functioning (i.e., play competence, language development, and social adaptation) and maternal behavior (i.e., encouragement of attention to the environment and I.Q.) are being obtained, thereby permitting examination of associations between aspects of mother-infant interaction in early infancy and the development of important aspects of cognitive and social competencies in the second year. At 48 months, a second follow-up will examine children's abilities that index representational competence, problem solving, reasoning skills, mathematical ability, language use and discourse, and selected aspects of generally adaptive behavior. In an ancillary investigation, methodological issues associated with the measurement of symbolic activity in young children are being studied. Although symbolic activities, such as language and pretense play, have traditionally been considered to be key indices of early developmental growth and competence, serious methodological issues surrounding their definition and measurement exist. In the present study, the effects of situational setting, social context, and assessment technique on children's interaction and language and play performance during the second year of life will be investigated.